The present invention relates to a positive-working radiation-sensitive mixture containing
(a) a compound that forms strong acid on exposure to actinic radiation, PA1 (b) a compound that contains at least one acid-cleavable C--O--C or C--O--Si bond, and PA1 (c) a water-insoluble polymeric binder that is soluble or at least swellable in aqueous-alkaline solutions. PA1 (a) a compound that forms strong acid on exposure to actinic radiation, PA1 (b) a compound that contains at least one acid-cleavable C--O--C or C--O--Si bond, and PA1 (c) a water-insoluble polymeric binder that is soluble or at least swellable in aqueous alkaline solutions,
The invention also relates to a radiation-sensitive recording material produced therewith that is suitable for producing photoresists, electronic components or printing plates, or for chemical milling.
The constant reduction in size of structures, for example, in chip production, down to the range of less than 1 .mu.m requires modified lithographic techniques. In order to image such fine structures, radiation is used that has a short wavelength, such as high-energy UV light, electron beams and X-rays. The radiation-sensitive mixture must be suited to the short-wave radiation. A summary of the requirements imposed on the radiation-sensitive mixture is provided in the paper by C. G. Willson entitled "Organic Resist Materials--Theory and Chemistry" [Introduction to Microlithography, Theory, Materials, and Processing, edited by L. F. Thompson, C. G. Willson, and M. J. Bowden, ACS Symp. Ser., 219:87 (1983), American Chemical Society, Washington]. There is therefore an increased requirement for radiation-sensitive mixtures that can be used in the more recent technologies such as mid- or deep-UV lithography [exposure, for example, using excimer lasers at wavelengths of 305 nm (XeF), 248 nm (KrF), 193 nm (ArF)], and electron-beam lithography or X-ray lithography. Preferably these mixtures are also sensitive over a wide spectral range and can be used in conventional UV lithography.
Mixtures that contain as essential constituents a component that forms a strong acid on exposure to actinic radiation and an acid-cleavable compound, for example, containing C--O--C or C--O--Si bonds, in addition to a water-insoluble binder that is soluble or at least swellable in aqueous alkaline solutions, are disclosed in DE 23 06 248 (=U.S. Pat. No. 3,779,778).
As compounds that form a strong acid on irradiation, use particularly has been made of onium salts such as diazonium, phosphonium, sulfonium or iodonium salts of non-nucleophilic acids, such as HSbF.sub.6, HAsF.sub.6, or HPF.sub.6 [J. V. Crivello, Polym. Eng. Sci., 23:953 (1983)]. In addition, halogen compounds, particularly trichloromethyltriazine derivatives or trichloromethyloxadiazole derivatives, o-(quinone diazide)sulfonyl chlorides, o-(quinone diazide)-4-sulfonic acid esters, organometal/organohalogen combinations, bis(sulfonyl)diazomethane, sulfonylcarbonyldiazomethane (DE 39 30 087) or nitrobenzyl tosylates [F. M. Houlihan et al., SPIE Proc., Adv. in Resist Techn. and Proc. 920:67 (1988)]have been recommended.
These compounds are used in negative- or positive-working radiation-sensitive mixtures. The use of these photolytic acid formers, however, entails certain disadvantages that severely restrict their possible uses in various fields of application. For example, many of the onium salts are toxic. Their solubility in many solvents is inadequate, and for this reason only a few solvents are suitable for producing a coating solution. In addition, impurity atoms, some of which are undesirable and which may result in process interferences, particularly in microlithography, are introduced if onium salts are used. Halogen compounds such as (quinone diazide)sulfonyl chlorides form strong hydrohalic acids, but on certain substrates they have only a limited durability. This has been improved by inserting an interlayer between substrate and radiation-sensitive layer containing compounds of the type (a), but this resulted in an undesirable increase in defects and in a reduced reproducibility (DE 36 21 376 =U.S. Pat. No. 4,840,867).
Although other classes of compounds that generate hydrohalic acid such as bis- (EP 137 452 =U.S. Pat. Nos. 4,619,998/4,696,888) or tristrichloromethyltriazines have a good acid-forming efficiency, they have an often inadequate solubility in common resist solvents. They are frequently sweated out of the photosensitive mixtures under processing conditions applied in practice, with the result that a reproducible production of the resultant layer is no longer possible.
The more recent publications by F. M. Houlihan et al., SPIE 920:67 (1988) show that, in addition to the above-mentioned acid formers, nitrobenzyl tosylates that form sulfonic acids with low migration tendency on exposure can also be used in certain positive-working, acid-labile resist formulations. From this it can be deduced that such compounds can also be used for photocurable systems. The sensitivities achieved under these circumstances and the thermal stability of the photoresist prove, however, to be inadequate.
Also known are resist formulations containing (naphthoquinone 2-diazide)-4-sulfonic acid esters, oximesulfonates, 1,2-disulfones, bissulfonyldiazomethane (DE 39 30 086) and sulfonylcarbonyldiazomethane (DE 30 30 087). All of these compounds have unsatisfactory quantum yields on exposure to actinic radiation. The resist formulations absorb radiation of the wavelength 248 nm to an appreciable extent. The sensitivity to radiation of this wavelength is in the range from 50 to 100 mJ/cm.sup.2. Practical structures having a size of 0.5 .mu.m and less cannot be imaged with such resists.
Despite the intensive research activity carried out in this field, no radiation-sensitive mixture is known at the present time with which it is possible to produce a positive-working radiation-sensitive recording material that has a high sensitivity in the deep LrV region (200 to 300 nm), that has a high resolution, that even with brief irradiation releases a sufficient amount of an acid that is strong enough to cleave compounds of the type (b), and that is still capable of being developed in aqueous alkali and is fully compatible with standard processing conditions.